1. Field of the Invention
The present invention relates to an image data memory device useful in a computer system, and more particularly to an image data memory device comprising a plurality of image memories.
2. Description of the Prior Art
FIG. 6 shows a prior art image data memory device capable of storing image data together with process control data added to the respective data. Hereinafter, process control data are often referred to merely as "control data".
The image data memory device shown in FIG. 6 comprises two image data memories 62 and 63, and an image processor 64. In the image data memories 62 and 63, using an image data signal 6b, image data can be written to and read from the coordinates specified by an image address signal 6a output from a central processing unit 61. The image processor 64 receives image output signals 6c and 6d from the respective image data memories 62 and 63, and performs the processing dictated by a control data output signal 6e contained in the image output signal 6c, on the image data entered by way of the image output signals 6c and 6d. The processing result is output as a processed image signal 6f which is supplied to a suitable display apparatus (not shown) through a display controller 65. In this configuration, the image date and the control data associated with each pixel of the image data are stored in one of the image data memories 62 and 63 (in this example, in the image data memory 62).
When the image data memory 62 can store n-bit data for every pixel, m bits out of the n bits (m&lt;n) are assigned for storing the control data, thus storing together the image data and control data. The m bits in the n-bit image output signal 6c are supplied as the control data output signal 6e to the image processor 64 to control the image processing. In the image data memory 62, as shown in FIG. 7, m bits out of the n bits of data that can be stored at one address are assigned to the control data. Therefore, when writing data to the image data memory 62, date created by combining the image data with the control data associated with the image data is written into the image data memory 62 by specifying the coordinates using the image address signal 6a.
FIG. 8 shows another prior art image data memory device. The image data memory device shown in FIG. 8 comprises two image data memories 82 and 83, a control data memory 84, and an image processor 85. In the image data memories 82 and 83, using an image data signal 8b, image data can be written to and read from the coordinates specified by an image address signal 8a supplied from a central processing unit 81. In the control data memory 84, using the image data signal 8b, a control data can be written to and read from the coordinates specified by the image address signal 8a supplied from the central processing unit 81. The image processor 85 receives image output signals 8c and 8d from the image data memories 82 and 83, and a control date output signal 8e from the control data memory 84. The image processor 85 performs the processing dictated by the control data output signal 8e on each pixel of image data entered by way of the image output signals 8c and 8d, and outputs the processing result as a processed image signal 8f which is supplied to a suitable display apparatus (not shown) through a display controller 86.
As shown in FIG. 9, the image data memories 82 and 83 and the control data memory 84 have independent address spaces. In the example shown in FIG. 9, the image data memories 82 and 83 store 32 bits per pixel and the control data memory 84 stores 2 bits per pixel. To write an image data and the associated control data, first the coordinates at which the image data is stored (i.e. one of the addresses assigned to the image data memory 82 or 83 (Oh-3fffffh or 4000OOh-7fffffh)) are specified using the image address signal 8a, and the image data supplied via the image data signal 8b is written to the specified coordinates. Thereafter, the corresponding coordinates (800000h-81ffffh) in the control data memory 84 are specified using the image address signal 8a, and the control data supplied via the image data signal 8b is written to the specified coordinates. Writing image data to the image data memories 82 and 83 and writing a control data to the control data memory 84 are thus performed sequentially and independently of each other.
Such prior art image data memory devices have drawbacks which will be described below.
In the image data memory device of FIG. 6, it is assumed that the image data memory 62 can store 8-bit data (256 colors) for each pixel (i.e., n=8). If two bits (providing four varieties) are needed for storing the control data for each pixel, two bits out of the eight bits must be assigned for storing the control data in the image data memory 62 (i.e., m=2), leaving six bits (64 colors) available for the image data for one pixel. Accordingly, the number of colors available for image display decreases. Furthermore, each time the need arises to write an image data into the image data memory 62 at the coordinates specified by the image address signal 6a, it is necessary to create the image data signal 6b by combining the image data and the control data, thus requiring extra processing. Moreover, when it is desired to read out or write only the control data, the image data, which is not the object of readout or writing, must be read out or written simultaneously with the control data. More specifically, when reading out, the data at the specified coordinates is read out from the image data memory 62, and the control data portion must be extracted from the read-out data, and when writing, first the image data is read out from the image data memory 62, and then the control data to be written is substituted into the control data portion of the read-out image data and the data thus rewritten is then put back into the image data memory 62. As described, even when reading out or writing only the control data, the image data must always be read out and the control data must be separated from or substituted into the image data, thus increasing the processing time.
In the image data memory device of FIG. 8, writing an image data into the image data memories 82 and writing the control date assigned to the image data are performed as described below. First, the image data entered via the image data signal 8b is written into the image data memory 82 at the coordinates specified by the image address signal 8a. Next, the control data entered via the image data signal 8b is written into the control data memory 84 at the same coordinates specified by the image address signal 8a. Thus, two writing processes, one to the image data memory 82 and one to the control data memory 84, are required for every writing of an image data. Therefore, the read/write software for an image data memory of this configuration becomes complicated since it must manage the coordinates in both the image data memories 82 and 83 and the control data memory 84, i.e., such software must perform the clipping of the drawing area or the like in processing.
When an image data and a control data corresponding thereto are moved within the image data memory device of FIG. 8, there arises the following problem. It is assumed that the image data memories 82 and 83 and the control data memory 84 stores image data and control data as shown in (a) of FIG. 10, respectively, and that, as a result of the process of the image processor in accordance with the control data stored in the rectangular area of the control data memory 84, the rectangular area of the image data memory 83 is displayed as shown by the reference numeral 104 in (a) of FIG. 10. Namely, the control data stored in the control data memory 84 indicates that in the rectangular area the image data stored in the image data memory 83 is to be displayed. When the rectangular area of the display 104 is to be moved, both the rectangular areas of the image data memory 83 and control data memory 84 are moved so that the image data moved in the image data memory 83 remain to be displayed after this moving process.
This moving process in the prior art will be described with reference to FIG. 10 in which numerals 101, 102, 103 and 104 respectively indicate the contents of the memories 82-84 and the display. First, the image data stored in the rectangular area of the image data memory 83 are moved. As a result of this movement, the contents of the memories 83 and 84 are changed as shown by reference numerals 102 and 103 in (b) of FIG. 10. As shown by numeral 104 in (b) of FIG. 10, the contents of the image date memory 83 come to disagree with those of the control data memory 84, resulting in that the image on the way of moving data appears on the display. Then, the control data stored in the rectangular area of the control data memory 84 are moved as shown in the block 103 of (c) of FIG. 10, and the display becomes as shown in the block 104 of (c) of FIG. 10 to indicate the image data in the rectangular area in the image data memory 83, thereby completing the movement of the image data and the change of the displayed position of the image data in the display. In this way, in the course of moving image data and control data corresponding thereto, the displayed contents disagree with the contents of the control data memory 84.